The present disclosure relates to an image processing apparatus and method, and more particularly, to an image processing apparatus and method that are capable of suppressing quantization error.
In the related art, bit transform techniques for performing transforms from a high bit depth to a low bit depth have usually been used as a quantization technique for image processing or the like. In other words, an N-bit image is transformed into an L-bit image (N>L) by a quantization process. On the other hand, an inverse transform process from a low bit depth to a high bit depth corresponds to inverse quantization. A linear quantization technique has usually been used as an image quantization technique. However, the linear quantization technique is low in computation cost but relatively large in a quantization error. For this reason, when an image of a high bit depth is transformed into an image of a low bit depth by quantization, and then the image of the low bit depth is transformed back into the image of the high bit depth by inverse quantization (is returned to an original bit depth), the restored image of the high bit depth (the image which has been subjected to the quantization and inverse quantization processes) may exhibit substantial deterioration compared to the original image (the image prior to the quantization and inverse quantization processes).
In this regard, a Lloyd-Max quantization technique has been proposed (for example, see Lloyd, “Least squares quantization in PCM”, IEEE Transactions, Information Theory, vol. IT-28, no. 2, pp. 129-137, March 1982). Generally, the Lloyd-Max quantization technique has been known as a quantization technique which results in little image distortion.